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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#SYNOPSIS">SYNOPSIS</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a></li>
  <li><a href="#RETURN-VALUES">RETURN VALUES</a></li>
  <li><a href="#BUGS">BUGS</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#HISTORY">HISTORY</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>EVP_RSA_gen, RSA_generate_key_ex, RSA_generate_key, RSA_generate_multi_prime_key - generate RSA key pair</p>

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code>#include &lt;openssl/rsa.h&gt;

EVP_PKEY *EVP_RSA_gen(unsigned int bits);</code></pre>

<p>The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining <b>OPENSSL_API_COMPAT</b> with a suitable version value, see <a href="../man7/openssl_user_macros.html">openssl_user_macros(7)</a>:</p>

<pre><code>int RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
int RSA_generate_multi_prime_key(RSA *rsa, int bits, int primes, BIGNUM *e, BN_GENCB *cb);</code></pre>

<p>The following function has been deprecated since OpenSSL 0.9.8, and can be hidden entirely by defining <b>OPENSSL_API_COMPAT</b> with a suitable version value, see <a href="../man7/openssl_user_macros.html">openssl_user_macros(7)</a>:</p>

<pre><code>RSA *RSA_generate_key(int bits, unsigned long e,
                      void (*callback)(int, int, void *), void *cb_arg);</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>EVP_RSA_gen() generates a new RSA key pair with modulus size <i>bits</i>.</p>

<p>All of the functions described below are deprecated. Applications should instead use EVP_RSA_gen(), <a href="../man3/EVP_PKEY_Q_keygen.html">EVP_PKEY_Q_keygen(3)</a>, or <a href="../man3/EVP_PKEY_keygen_init.html">EVP_PKEY_keygen_init(3)</a> and <a href="../man3/EVP_PKEY_keygen.html">EVP_PKEY_keygen(3)</a>.</p>

<p>RSA_generate_key_ex() generates a 2-prime RSA key pair and stores it in the <b>RSA</b> structure provided in <i>rsa</i>.</p>

<p>RSA_generate_multi_prime_key() generates a multi-prime RSA key pair and stores it in the <b>RSA</b> structure provided in <i>rsa</i>. The number of primes is given by the <i>primes</i> parameter. If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see <a href="../man7/RAND.html">RAND(7)</a>), the operation will fail.</p>

<p>The modulus size will be of length <i>bits</i>, the number of primes to form the modulus will be <i>primes</i>, and the public exponent will be <i>e</i>. Key sizes with <i>num</i> &lt; 1024 should be considered insecure. The exponent is an odd number, typically 3, 17 or 65537.</p>

<p>In order to maintain adequate security level, the maximum number of permitted <i>primes</i> depends on modulus bit length:</p>

<pre><code>&lt;1024 | &gt;=1024 | &gt;=4096 | &gt;=8192
------+--------+--------+-------
  2   |   3    |   4    |   5</code></pre>

<p>A callback function may be used to provide feedback about the progress of the key generation. If <i>cb</i> is not NULL, it will be called as follows using the BN_GENCB_call() function described on the <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a> page.</p>

<p>RSA_generate_key() is similar to RSA_generate_key_ex() but expects an old-style callback function; see <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a> for information on the old-style callback.</p>

<ul>

<li><p>While a random prime number is generated, it is called as described in <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a>.</p>

</li>
<li><p>When the n-th randomly generated prime is rejected as not suitable for the key, <i>BN_GENCB_call(cb, 2, n)</i> is called.</p>

</li>
<li><p>When a random p has been found with p-1 relatively prime to <i>e</i>, it is called as <i>BN_GENCB_call(cb, 3, 0)</i>.</p>

</li>
</ul>

<p>The process is then repeated for prime q and other primes (if any) with <i>BN_GENCB_call(cb, 3, i)</i> where <i>i</i> indicates the i-th prime.</p>

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

<p>EVP_RSA_gen() returns an <i>EVP_PKEY</i> or NULL on failure.</p>

<p>RSA_generate_multi_prime_key() returns 1 on success or 0 on error. RSA_generate_key_ex() returns 1 on success or 0 on error. The error codes can be obtained by <a href="../man3/ERR_get_error.html">ERR_get_error(3)</a>.</p>

<p>RSA_generate_key() returns a pointer to the RSA structure or NULL if the key generation fails.</p>

<h1 id="BUGS">BUGS</h1>

<p><i>BN_GENCB_call(cb, 2, x)</i> is used with two different meanings.</p>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_PKEY_Q_keygen.html">EVP_PKEY_Q_keygen(3)</a> <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a>, <a href="../man3/ERR_get_error.html">ERR_get_error(3)</a>, <a href="../man3/RAND_bytes.html">RAND_bytes(3)</a>, <a href="../man7/RAND.html">RAND(7)</a></p>

<h1 id="HISTORY">HISTORY</h1>

<p>EVP_RSA_gen() was added in OpenSSL 3.0. All other functions described here were deprecated in OpenSSL 3.0. For replacement see <a href="../man7/EVP_PKEY-RSA.html">EVP_PKEY-RSA(7)</a>.</p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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